1. FIELD OF THE INVENTION
The present invention relates to an apparatus for cementless building of retreaded tires, and more particularly, to an apparatus that heats and applies cushion gum material to a tire casing.
2. DESCRIPTION OF RELATED ART
In a tire retreading process, a strip or web of rubber bonding material or cushion gum is applied to the periphery of a buffed tire casing. Typically a cement, such as a rubber/hydrocarbon solvent solution, is first applied to the tire casing to provide the necessary tack to firmly hold the cushion gum material to the tire casing during subsequent stitching, tread application, and curing. The step of applying cement is costly and time consuming because the cement must be applied and allowed to dry before the cushion gum material can be affixed. Additionally, the use of solvent based cements or adhesives can cause safety and environmental concerns.
The cement can be eliminated from the process by heating the cushion gum material because the tack of a rubber compound, such as the cushion gum material, increases as it is heated. One approach has been to warm entire rolls of the cushion gum in an oven. This approach, however, can cause a decrease in material shelf life due to the short scorch time of the cushion gum material. This is particularly a problem if the material is not used promptly after heating.
Another approach has been to heat the cushion gum material as it is being applied to the tire casing. For example, see U.S. Pat. No. 4,096,008, the disclosure of which is expressly incorporated herein in its entirety by reference, disclosing a method of manufacturing and retreading tires. The cushion gum material is pulled from a supply roll, heated at an outer surface, pulled around and applied to the tire casing, and subsequently pressured by rollers to the tire casing. Heating the cushion gum material at an outer surface to increase the amount of tack at an inner surface can result in overheating or scorching the cushion gum material. Additionally, tensioning the cushion gum material can stretch the cushion gum material and result in an uneven thickness. Furthermore, applying and pressuring the cushion gum to the tire casing in separate steps can result in entrapped air between the tire casing and the cushion gum material. Accordingly, there is a need in the art for an improved apparatus for cementless building of retreaded tires.